The invention concerns a device for dry-forming a fibrous web.
For the production of nonwovens it is known that the fibers are deposited by means of an air flow onto a deposit belt to form a fibrous layer. This method, typically referred to in the field as an airlaid method is based on the fibers or fiber mixtures being deposited such that they are uniformly distributed by means of a forming head onto the upper surface of a deposit belt. The zone covered by the forming head on the deposit belt is normally referred to as the forming zone, in which the fibers are joined on the deposit belt.
A device of this type is known, for example, from EP 0 006 696 A1.
With the known devices, a plurality of fibers or fiber mixtures is supplied by means of an air flow to a forming head. Means are provided within the forming head for mixing and distributing the fibers. A forming outlet is formed on the bottom surface of the forming head, which is typically disposed at a short spacing above the deposit belt. As a result, an empty space is formed between the forming head and the deposit belt, which serves for the supplying of a fiber flow exiting the forming outlet. The depositing of the fibers onto the deposit belt is supported by a suction device, which receives and discharges the air from the fiber flow. The fibrous layer formed on the upper surface of the deposit belt is continuously transported out of the forming zone via the deposit belt, such that a fibrous layer is obtained, which is subsequently supplied to a further processing, such as a solidification process, for example.
The depositing of the fibers is substantially determined by the air flow generated in the forming zone. With the known device, the forming head is on the entry end of the deposit belt, and sealing means in the form of sealing rollers are disposed at the output end of the deposit belt, respectively, in order to shield the empty space formed between the forming outlet and the deposit belt from the surrounding environment. The sealing rollers work together with housing components disposed on the longitudinal surfaces of the deposit belt in order, thereby, to prevent the entry of secondary air flows from the surrounding environment. In practice, however, it has been the case that depending on the type of fiber, and the size of the fiber, irregularities arise in the depositing of the fibers, which are referred to as so-called cloud formations. In this respect, it is believed that the suction flows generated by the suction device may lead to irregularities in the fiber deposit.
In order to eliminate irregularities of this type in the depositing of the fibers, it is known, for example, from WO 2006/131122 A1, to influence the suction flow of the suction device in sub-sections of the forming zone. With the known device, a baffle is associated with an entry end of the forming zone of the suction device, which influences the suction flow beneath the deposit belt. As a result, air turbulence at the entry end of the forming zone, in particular, which occurs as a result of secondary air from the surrounding environment being suctioned into this area, is prevented. As a result, however, varying suction flows occur in the forming zone, which lead to differing deposit behaviors of the fibers within the forming zone.